Follicular Carcinoma

Follicular carcinomas are the second most common form of thyroid cancer, accounting for 10% to 20% of all thyroid cancers. They tend to present in women, and at an older age than do

papillary carcinomas, with a peak incidence in the forties and fifties. The incidence of follicular carcinoma is increased in areas of dietary iodine deficiency, suggesting that in some

cases, nodular goiter may predispose to the development of the neoplasm. The high frequency of RAS mutations in follicular adenomas and carcinomas suggests that the two may be

related tumors.

Morphology.

Follicular carcinomas are single nodules that may be well circumscribed or widely infiltrative ( Fig. 24-18 ). Sharply demarcated lesions may be exceedingly difficult to distinguish from

follicular adenomas by gross examination. Larger lesions may penetrate the capsule and infiltrate well beyond the thyroid capsule into the adjacent neck. They are gray to tan to pink on

cut section and, on occasion, are somewhat translucent when large, colloid-filled follicles are present. Degenerative changes, such as central fibrosis and foci of calcification, are

sometimes present.

Microscopically, most follicular carcinomas are composed of fairly uniform cells forming small follicles containing colloid, quite reminiscent of normal thyroid ( Fig. 24-19 ). In other

cases, follicular differentiation may be less apparent, and there may be nests

Figure 24-18Follicular carcinoma. Cut surface of a follicular carcinoma with substantial replacement of the lobe of the thyroid. The tumor has a light-tan appearance and contains small

foci of hemorrhage.

Figure 24-19Follicular carcinoma of the thyroid. A few of the glandular lumens contain recognizable colloid.

Figure 24-20Capsular integrity in follicular neoplasms. Evaluating the integrity of the capsule is critical in distinguishing follicular adenomas from follicular carcinomas. In adenomas

(A), a fibrous capsule, usually thin but occasionally more prominent, circumferentially surrounds the neoplastic follicles and no capsular invasion is seen (arrowheads); compressed

normal thyroid parenchyma is usually present external to the capsule (top of the panel). In contrast, follicular carcinomas demonstrate capsular invasion (B, arrow-heads) that may be

minimal, as in this case, or widespread with extension into local structures of the neck. The presence of vascular invasion is another feature of follicular carcinomas.

Figure 24-21Medullary carcinoma of thyroid. These tumors typically show a solid pattern of growth and do not have connective tissue capsules. (Courtesy of Dr. Joseph Corson,

Brigham and Women's Hospital, Boston, MA.)

Figure 24-22Medullary carcinoma of the thyroid. These tumors typically contain amyloid, visible here as homogeneous extracellular material, derived from calcitonin molecules

secreted by the neoplastic cells.

Figure 24-23Electron micrograph of medullary thyroid carcinoma. These cells contain membrane-bound secretory granules that are the sites of storage of calcitonin and other peptides

(30,000X).

Figure 24-24Parathyroid adenomas are almost always solitary lesions. Technetium-99m-sestamibi radionuclide scan demonstrates an area of increased uptake corresponding to the left

inferior parathyroid gland (arrow). This patient had a parathyroid adenoma. Preoperative scintigraphy is useful in localizing and distinguishing adenomas from parathyroid hyperplasia,

where more than one gland would demonstrate increased uptake.

Figure 24-25Parathyroid adenoma. A, Solitary chief cell parathyroid adenoma (low-power photomicrograph) revealing clear delineation from the residual gland below. B, High-power

detail of a chief cell parathyroid adenoma. There is some slight variation in nuclear size but no anaplasia and some slight tendency to follicular formation.

TABLE 24-5-- Causes of Hypercalcemia

Date: 2016-04-22; view: 642